The present invention relates to a color display device for a fish detection sonar capable of displaying the targets such as the surface and bottom of the sea and detected schools of fish in different colors.
One of the display devices widely used in the fish detection sonars is of the so-called "flasher type" comprising a rotary disk driven at a constant rotational speed, a fixed scale disk disposed coaxially of and in opposed relation with the rotary disk, and a display element such as a neon bulb attached upon the rotary disk. The rotation of the rotary disk is synchronized with the emission of ultrasonic pulses by a sonar transducer. That is, the time required for the rotary disk to make one complete rotation is equal to the pulse spacing. A sonar receiver receives the pulses at the instant they are transmitted so that the display element may be turned on to display the surface of the sea. The sonar receiver also receives the echo pulses reflected from the bottom of the sea and the schools of fish in the sea so that the display element may be also turned on to display the bottom and fish. There is a time interval between the displays of the surface and botton of the sea and the schools of fish that are detected so that the ranges or distances from the sea surface to the bottom and the schools of fish may be detected.
However, the prior art display device of the type described has a distinct defect in that a viewer tends to misinterpret very frequently the targets because the surface and bottom of the sea and schools of fish detected are displayed by monochrome light.